Evaluation of the effects of RP5063, a novel, multimodal, serotonin receptor modulator, as single-agent therapy and co-administrated with sildenafil, bosentan, and treprostinil in a monocrotaline-induced pulmonary arterial hypertension rat model.

Pulmonary arterial hypertension (PAH), a condition that is defined by pulmonary vasculature constriction and remodeling, involves dysfunctional signaling of the serotonin (5-HT) receptors, 5-HT2A/2B/7. In a rat model of monocrotaline (MCT)-induced PAH, the effectiveness of RP5063 (RP), a dopamine and 5-HT receptor modulator, was evaluated as monotherapy and as an adjunct to standard PAH treatments. After a single 60 mg/kg dose of MCT, rats received vehicle (MCT+Veh; gavage twice-daily [b.i.d.]), RP (10 mg/kg; gavage b.i.d.), bosentan (B; 100 mg/kg; gavage BID), sildenafil (S; 50 mg/kg; gavage, BID), treprostinil (T; 100 ng/kg/min over 24 h intravenous), RP+B, RP+S, and RP+T for 28 days. Single-agent RP limited the functional and structural effects of PAH seen in the MCT+Veh group, with significant improvements in pulmonary hemodynamics, right ventricular (RV) hypertrophy, SO2, and pulmonary blood vessel structural changes. These effects appeared comparable with those associated with B, S, and T. Adjunctive RP treatment resulted in significantly lower mean pulmonary arterial pressures, RV systolic pressure. It also improved SO2 measurements, as compared with MCT+Veh (P < 0.05), and diastolic pulmonary artery pressure (P < 0.05), as compared with single-agent B and S therapy (Bonferroni method adjusting for multiplicity). RP+S appeared to show the most consistent and extensive effects on pulmonary hemodynamics, respiratory parameters, and histopathologic changes. These results corroborate earlier preclinical findings supporting the efficacy of single-agent RP in PAH. RP, as mono and adjunctive therapy compared with induced-control, mitigated the functional and structural effects of MCT-induced PAH.

Preclinical Pharmacology and Pharmacokinetics of Inhaled Hexadecyl-Treprostinil (C16TR), a Pulmonary Vasodilator Prodrug.

This article describes the preclinical pharmacology and pharmacokinetics (PK) of hexadecyl-treprostinil (C16TR), a prodrug of treprostinil (TRE), formulated in a lipid nanoparticle (LNP) for inhalation as a pulmonary vasodilator. C16TR showed no activity (>10 µM) in receptor binding and enzyme inhibition assays, including binding to prostaglandin E2 receptor 2, prostaglandin D2 receptor 1, prostaglandin I2 receptor, and prostaglandin E2 receptor 4; TRE potently bound to each of these prostanoid receptors. C16TR had no effect (up to 200 nM) on platelet aggregation induced by ADP in rat blood. In hypoxia-challenged rats, inhaled C16TR-LNP produced dose-dependent (0.06-6 µg/kg), sustained pulmonary vasodilation over 3 hours; inhaled TRE (6 µg/kg) was active at earlier times but lost its effect by 3 hours. Single- and multiple-dose PK studies of inhaled C16TR-LNP in rats showed proportionate dose-dependent increases in TRE Cmax and area under the curve (AUC) for both plasma and lung; similar results were observed for dog plasma levels in single-dose PK studies. In both species, inhaled C16TR-LNP yielded prolonged plasma TRE levels and a lower plasma TRE Cmax compared with inhaled TRE. Inhaled C16TR-LNP was well tolerated in rats and dogs; TRE-related side effects included cough, respiratory tract irritation, and emesis and were seen only after high inhaled doses of C16TR-LNP in dogs. In guinea pigs, inhaled TRE (30 µg/ml) consistently produced cough, but C16TR-LNP (30 µg/ml) elicited no effect. These results demonstrate that C16TR-LNP provides long-acting pulmonary vasodilation, is well tolerated in animal studies, and may necessitate less frequent dosing than inhaled TRE with possibly fewer side effects.

RP5063, a novel, multimodal, serotonin receptor modulator, prevents monocrotaline-induced pulmonary arterial hypertension in rats.

Pulmonary arterial hypertension (PAH), a condition characterized by pulmonary vasculature constriction and remodeling, involves dysregulation of the serotonin (5-HT) receptors 5-HT2A and 5-HT2B. A rat model of monocrotaline (MCT)-induced PAH was used to examine the potential beneficial effects of RP5063, a 5-HT receptor modulator. After a single 60mg/kg dose of MCT, rats were gavaged twice-daily (b.i.d.) with vehicle, RP5063 (1, 3, or 10mg/kg), or sildenafil (50mg/kg) for 28 days. RP5063 at a dose as low as 1mg/kg, b.i.d. reduced pulmonary resistance and increased systemic blood oxygen saturation. The highest dose of RP5063 (10mg/kg, b.i.d.) reduced diastolic, systolic, and mean pulmonary pressure, right systolic ventricular pressure, ventilatory pressure, and Fulton's index (ratio of right to left ventricular weight). Doses as low as 3mg/kg RP5063, b.i.d. also increased weight gain and body temperature, suggesting an improvement in overall health of MCT-treated animals. Similar reductions in pulmonary, right ventricular, and ventilatory pressure, pulmonary resistance, and Fulton's index as well as increased systemic blood oxygen saturation were observed in animals treated with the reference agent sildenafil at a higher dose (50mg/kg, b.i.d.). Histological examination revealed that RP5063 produced dose-dependent reductions in pulmonary blood vessel wall thickness and proportion of muscular vessels, similar to sildenafil. RP5063 completely blocked MCT-induced increases in the plasma cytokines TNFα, IL-1ß, and IL-6 at all doses. In summary, RP5063 improved pulmonary vascular pathology and hemodynamics, right ventricular pressure and hypertrophy, systemic oxygen saturation, and overall health of rats treated with MCT.

RP5063, a novel, multimodal, serotonin receptor modulator, prevents Sugen 5416-hypoxia-induced pulmonary arterial hypertension in rats.

RP5063, a multimodal dopamine (DA) and serotonin (5-HT) modulator with high affinity for DA2/3/4 and 5-HT2A/2B/7 receptors and moderate affinity for SERT, is a novel therapeutic of special interest in the treatment of pulmonary arterial hypertension (PAH). Evidence indicates that therapeutics targeting the 5-HT2A/2B receptors can influence the pathogenesis of PAH. However, the therapeutic effect of RP5063 in humans has yet to be investigated. A Sugen 5416-hypoxia (SuHx)-induced PAH model was used to evaluate twice-daily (b.i.d.) RP5063 at 10mg/kg (RP-10) and 20mg/kg (RP-20), as compared with positive (sildenafil 50mg/kg b.i.d.; Sil-50) and negative controls (SuHx+vehicle; SuHx+veh), in 24 adult male Wistar-Kyoto rats. RP5063 showed significantly lower systolic pulmonary arterial (both doses) and systolic right ventricular (RP-10) pressures, and improvement in oxygen saturation (RP-20). It significantly reduced small-vessel wall thickness (RP-20), lowered the percentage of muscular vessels (both doses). Both doses limited arterial obliteration due to endothelial cell proliferation, prevented plexiform lesion formation, and stemmed the release of leukotriene B4. Sildenafil showed statistically greater effects on vessel structure than that seen in both RP5063 groups and improved oxygen saturation. Additionally, Sildenafil did not demonstrate any significant effect on arterial obliteration, plexiform lesion development, or pulmonary arterial or right ventricular pressure. As PAH gains in severity, the impact of RP5063 inhibition of 5HT2B increases, preventing arterial constriction and improving pulmonary hemodynamics. Due to its functional, structural, and chemokine effects, RP5063 represents a promising candidate for investigation in late-phase PAH.

Induced growth and maturation of the gastrointestinal tract after Phaseolus vulgaris lectin exposure in suckling rats.

OBJECTIVES: In mammals, the postnatal development of the gastrointestinal tract is characterized by vast structural and functional changes. Using a suckling rat model, we investigated whether red kidney bean lectin, phytohemagglutinin (PHA), a potent gut mitogen in adult rats, can accelerate the growth and maturation of the gastrointestinal tract. METHODS: At either 10 or 14 days of age, suckling rats were daily gavage fed with PHA (0.05 mg/g body weight) or saline for 3 days. At 1 or 3 days after this treatment, gastrointestinal organ growth, intestinal morphology, disaccharidase pattern, macromolecular absorption capacity, and pancreatic enzyme contents were studied. RESULTS: After PHA exposure, increased small intestinal growth and number of crypt cells were observed, whereas the proportion of enterocytes with supranuclear vacuoles in the distal intestine was decreased. The macromolecular absorption of the markers bovine immunoglobulin (Ig)G and bovine serum albumin and plasma levels of maternal IgG decreased, and intestinal disaccharidases switched toward an adult-like pattern. The pancreas weight and pancreatic protein and trypsin contents increased. These changes were partly reversible when the PHA treatment began at 10 days of age, but they persisted when the treatment began at 14 days of age. CONCLUSIONS: PHA induced enhanced growth and precocious functional maturation of the gastrointestinal tract in suckling rats. The effects persisted if the PHA treatment started at 14 days of age, but not before, suggesting an age dependent mechanism. These findings may lead to a better understanding of gastrointestinal maturation and constitute a basis for the treatment of mammals having an immature gut.

What are the pancreatic target cells for gastrin and its CCKB receptor? Is this a couple for cancerous cells?

The objectives of this review are to summarize, analyse and discuss the roles played by the CCK receptor subtypes and their agonists on pancreatic enzyme secretion, pancreas growth and regeneration, define the receptors specific target cells and evaluate the role of gastrin in pancreatic pathologies including cancer. In rodents, it is clear that the CCKARs present on pancreatic acinar cells play a major role in enzyme secretion. In large mammals, CCK does not seem to be the final mediator of enzyme release. In rat, gastrin and its CCKBR seem responsible for foetal pancreas growth while after birth, CCK was shown to be the most potent trophic factor via occupation of its CCKAR. In pig and human, no one has yet established a direct link between CCK, gastrin and pancreas growth. In rodent's pancreas, the CCKAR were observed on acinar cells as well as on islet's alpha and beta cells; in six other species, the CCKAR were present only on alpha and beta cells with the CCKBR always present on delta cells. The CCKBRs were overexpressed in acute pancreatitis and in metaplastic pancreas following duct ligation. In pancreatic cancer cells, a gastrin autocrine loop involving the CCKBR was suggested. The presence of both CCKR-subtypes and gastrin was observed in many pancreatic tumors; however, their role in cancer growth remains controversial.

Bovine pancreatic secretion in the first week of life: potential involvement of intestinal CCK receptors.

The aim of this study was to evaluate pancreatic juice secretion of calves in the first postnatal days, and determine a potential involvement of cholecystokinin (CCK) and intestinal CCK receptor in its regulation. Nine neonatal Friesian calves (five controls and four treated intraduodenally with FK480, a CCK-A receptor antagonist) were surgically fitted with a pancreatic duct catheter and a duodenal cannula before the first colostrum feeding. Collections of pancreatic juice and duodenal luminal pressure recordings were started early after recovery from anaesthesia and continued for 6 days. From day 2 or 3 of life, periodic fluctuations in pancreatic secretions were observed in concert with duodenal myoelectric motor complex (MMC) and variations in plasma pancreatic polypeptide (PP) concentrations. Intraduodenal administration of FK480 reduced pancreatic juice secretion while intravenous infusion of CCK had no effect. Immunocytochemistry indicated an association of mucosal CCK-A and -B receptors with neural components of the small intestine. In conclusion, periodic activity of the exocrine pancreas exists in neonatal calves soon after birth and local neural intestinal CCK-A receptors could be partly responsible for the modulation of neonatal calf pancreatic secretion.

Small intestine growth and morphometry in piglets weaned at 7 days of age. effects of level of energy intake.

Two trials involving a total of 56 pigs were conducted to examine the effects of weaning at 7 d of age (trial 1) and of energy intake level and length of post-weaning underfeeding period (trial 2) on small intestinal (SI) development and morphometry. At 3 d after weaning, weight of the SI and mucosa (g/kg body weight) and villous height along SI were reduced by 20, 36 and 41%, respectively, compared to the day of weaning. Intestinal morphometrical changes are dependent on SI site and days post-weaning. Villous atrophy on d 3 and recovery on d 14 post-weaning were greater and occurred earlier in the proximal than in the medial and distal SI. Villous height was dependent on the level of energy intake which explains 56% of the variations in proximal SI villous height in weaned pigs and 73% when data of the sow-reared pigs were included in the analysis. Moreover, after 4 d of refeeding, underfed piglets showed similar villous characteristics to piglets fed a continuously high feeding level after weaning stressing that capacities of intestinal restoration were not affected by the length of the post-weaning underfeeding period. Overall, the present results suggest a spatial and temporal effect of weaning on villous atrophy and recovery, and that the level of energy intake is a major factor accounting for the post-weaning villous height.